Various kinds of bolts and nuts are used for fastening together various parts of a machine, whether it may be a common industrial machine or a machine designed for a specific purpose. When the bolts and nuts are removed to enable the inspection or replacement of any machine part, it is also usual to clean the screw threads of the bolts. The simplest method of cleaning any such bolt is to apply a wire brush or the like to its surface to remove stain or foreign matter therefrom. This kind of work has been done manually. There is also known a device which has been developed exclusively for cleaning a specific type of bolts efficiently.
Boilers, reactors, steam turbines and related equipments in steam or nuclear power plants are periodically inspected, either in accordance with law or voluntarily. The inspection includes not only the disassembling of the machine parts, but also the strict examination of the bolts and nuts. It is, for example, necessary to clean the bolts by removing any foreing matter from their screw threads and polishing them.
There is, however, a limit to the efficiency which can be achieved if the bolts are cleaned manually by means of an ordinary or rotary brush, or the like. The scattering of dust is unavoidable, even if a special cleaning device may be employed. It is necessary to keep any dust from rising, particularly in a nuclear power plant, since it is likely to result in a greater danger of radioactive contamination. Therefore, it is usual to, for example, set up a tent enclosing the place where any such cleaning work is done, and collect any rising dust into a disposal system by a blower. The cleaning work which makes it necessary to set up a tent whenever it is done is, however, far from efficient.
The bolts to be cleaned are removed from the machine parts and carried to the tent. If the bolts to be cleaned are of the type which cannot be brought to the tent, such as bolts embedded in a turbine casing, it is necessary to set up another tent enclosing the place where they exist. Even if a special cleaning device may be available, it is necessary to do any such cleaning work in a tent at the sacrifice of efficiency, as the device has no sealing mechanism that can prevent the scattering of dust.
The present applicant has filed Japanese Patent Application No. 238011/1987 which discloses a device designed for the efficient cleaning of bolts, etc. This device includes a sleeve in which the bolt to be cleaned is placed, and a rotor disposed therein and having a brush. The bolt is held by the rotor and is polished by the brush disposed on the peripheral surface of the rotor.
An arm is pivotally attached to the peripheral surface of the rotor. A centrifugal force acts on the arm when the rotor is rotated, and brings the brush into rubbing contact with the surface of the bolt. The arm forms the free end of the rotor and is, therefore, vibrated considerably when the rotor is rotated at a high speed. The arm forms a center of mass and is, therefore, likely to cause resonance, depending on its length and the rotating speed of the rotor. Its resonance results in a heavy vibration of the entire device. The vibration of the device not only imposes a great burden on a man holding it during a particular cleaning job, but also causes the generation of a large noise and is even likely to result in its own destruction.
If the cleaning device is rotated only in such a direction that the brush is moved in the direction opposite to the lead of a screw thread, the thread not only imparts a greater resistance to the operation of the device, but also causes it to vibrate to a greater extent. Therefore, in case that the brush is continuously contacted to the periphery of the bolt throughout the operation, if the direction of rotation of the brush differs from the lead of the screw thread, the resistance imposes a greater burden on the worker and gives him a greater amount of fatigue, while the vibration is undesirably transmitted to his hands. The continuance work of such operation will not be good for the health of the worker. A still greater burden is imposed on the worker who has to use a larger device for cleaning a larger bolt. When cleaning, for example, an upright embedded bolt, he has to move the device up and down. No efficiency can be expected from any work when he has to support the weight of the device manually.
If the brush is rotatable only in one direction, it always takes the same position when contacting the screw thread and can, therefore, clean only one flank thereof, while leaving the other flank thereof uncleaned.